This invention relates to the field of portable hand tools known as xe2x80x9clocking pliersxe2x80x9d, which allow adjustment of a set of opposable plier jaws which are pivotally fastened to one another, and are able to clamp and restrain a workpiece of variable size and geometry without continuous gripping effort from the operator.
A study of the prior art, such as U.S. Pat. Nos. 5,992,273 and 6,012,361, shows that those locking plier designs which have a thumbscrew means of adjustment require the use of two hands to achieve the adjustment. The operator uses one hand to hold the body of the pliers and uses a second hand to spin the thumbscrew to achieve the proper gap distance between jaws for clamping the workpiece. The solo operator has no hands available to hang on to the workpiece while the plier is adjusted to the proper jaw gap setting.
The significant advantage of the thumbscrew variation of a locking plier tool is the ability to continuously adjust the gap distance between the jaws of the tool. Properly adjusted, the linkage mechanism is able to exert very large clamping forces on the workpiece and lock the jaws in place to maintain a continuous clamping force on the workpiece without a constant grip force from the operator.
The rotational advance or retreat of the adjustment link coupled to the screw permits analog adjustment to be achieved over the entire range of workpiece sizes able to be clamped by the plier. A ball detent or pinion gear tooth adjustment is not truly practical for jaw adjustment of the tool as such methods limit adjustment to the discrete step size allowed by the resolution of the ball detents or the gear tool spacing. The rotary adjustment of a screw thread is preferred to achieve the correct jaw gap setting to clamp the workpiece. Many different locking plier designs recognize this important feature as is demonstrated not only by commercially available pliers such as the trade name VISE GRIP (R) locking plier, but also those of U.S. Pat. Nos. 6,199,458 B1 and 6,012,361. The only advantage in U.S. Pat. No. 6,012,361 is that the plier body length remains constant. The user must still perform the thumbscrew adjustment using two hands. U.S. Pat. No. 6,199,458 B1 also has this problem of two handed coarse adjustment. While U.S. Pat. No. 6,199,458 B1 has a thumb-accessible slide on one of the handles of the tool, this release slide actuator is not used for jaw gap adjustment before clamping but instead is used for releasing the grip of the tool on the workpiece when finished.
Warheit touches on the notion of a thumb digit means of adjustment in U.S. Pat. No. 6,095,019, but has no screw adjustment in his invention to effect the movement of the pivotable jaw. The coarse adjustment is effected by a guide plate and sliding wedge first slipping past each other for gap setting and then frictionally engaging once the gap size is set by the user via a control member. The assembly is not only costly and cumbersome to manufacture, but also allows the opportunity to jam and incapacitate the guide plate and sliding wedge piece parts of the tool with the introduction of grime in the slot channels of the control member.
The disclosed invention is a locking plier hand tool with an adjustment link for varying the opening between a fixed and a movable jaw of the tool, and includes a threaded shaft journaled between proximal and distal bearings, preferrably designed as bearing surfaces, and also includes a thumb dial, or adjustment dial, positioned distally to the adjustment link. Unlike the prior art, the screw adjustment means of the invention is found in the midbody of the tool, near the average user""s thumb location, instead of at the proximal end of the fixed handle. The threaded shaft is journaled on two bearing surfaces which gives more stability for smoother operation, and prevents misalignment between the shaft and the bearing surfaces within which it is held, which could cause jamming or difficulty rotating the thumb dial.
The advantage of the tool design is that it places a thumb dial in a distal position with respect to the adjustment link and also in a position that nearly approximates the location of an average user""s thumb when holding the tool, permitting single handed jaw opening adjustment through the use of the thumb digit. The single handed adjustment capability of the disclosed invention frees the other hand of the operator for workpiece manipulation during the gap adjustment or workpiece clamping operation.